Question: Simplify the following expression: $ a = 6 - \dfrac{3z - 9}{2} $
Answer: In order to subtract expressions, they must have a common denominator. Multiply the first expression by $\dfrac{2}{2}$ $ \dfrac{6}{1} \times \dfrac{2}{2} = \dfrac{12}{2} $ Therefore $ a = \dfrac{12}{2} - \dfrac{3z - 9}{2} $ Now the expressions have the same denominator we can simply subtract the numerators: $a = \dfrac{12 - (3z - 9) }{2} $ Distribute the negative sign: $a = \dfrac{12 - 3z + 9}{2}$ $a = \dfrac{-3z + 21}{2}$